JPS6021440A - Method for measuring distribution of local void rate - Google Patents

Abstract

PURPOSE:To measure the distribution of a local void rate accurately, by measuring a time when projection data is converged to a constant value in advance, and performing the measurement at this timing. CONSTITUTION:A density meter 118 for X rays or gamma rays is arranged so as to hold a pipe 111, in which a sample to be checked flows. A time, when projection data is converged into a constant value, is measured in advance by the density meter 118, and a collecting time of the projection data is determined. Based on the determined collecting time, a CT scanner device 112 is actuated and the measurement is started. Namely, a driving device 116 is controlled by a control device 117, a radiation source 113, which generates X rays or gamma rays, and a detector 114 are made to scan, and the distribution of a local void rate in the pipe 111 is measured. Thus the distribution of the local voik rate can be measured accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for measuring a local void fraction distribution of a gas-liquid two-phase flow in a nuclear reactor, for example.

[Technical background of the invention]

For example, it is extremely important for the design of nuclear reactor equipment to accurately measure the void fraction of gas-liquid two-phase flow in tubes in order to elucidate heat transfer flow phenomena in nuclear reactors. In gas-liquid two-phase flow, various flow patterns occur depending on the flow rate of each gas-liquid phase and the shape of the tube. At this time, the ratio of the area of the entire bubble to the area of the cross section of the tube is usually expressed as α, and this is called the void ratio.

One of the methods for measuring the void ratio is the conventional probe method. In this probe method, a probe with two electrodes at its tip is plunged into a two-phase flow, and the tip of the probe is brought into contact with a bubble by utilizing the difference in electrical type conductivity between the gas-liquid electrodes. This method calculates the local void rate from the time ratio.

In addition to the above-mentioned probe method, there is an X-ray transmission method. This X-ray transmission method will be explained with reference to FIG.

Reference numeral 1 in the figure indicates a flow path pipe through which a gas-liquid two-phase flow in which a gas phase and a liquid phase are mixed, such as a void V, flows.

An X-ray tube 2 is disposed at one side of the flow pipe 1 with a space therebetween, and a detector 3 and a counter 4 are disposed on the side facing the X-ray tube 2.

That is, the configuration is such that X-rays are irradiated from the X-ray tube 2 to transmit the gas-liquid two-phase flow, and the intensity of the transmitted X-rays is detected by the detector 3 and counted by the counter 4. For example, let the measured X-ray intensity be E, the measured X-ray intensity when only the liquid phase flows in the same flow path pipe 1 is ■, and similarly the measured X-ray intensity when only the gas phase V flows is ■, Then, the void ratio α is expressed by the following formula.

[Problems with background technology]

In the case of the above-mentioned probe method, since the probe is inserted into the gas-liquid two-phase flow, the internal flow is disturbed, and signal processing based on the electrical conductivity between the electrodes is difficult, making it difficult to perform accurate measurements. There wasn't. Although the X-ray transmission method has higher accuracy than the probe method, the calculated void ratio α is
This is the Dito ratio on the x' line, and is not the void ratio of the cross section of the flow path pipe 1 or the local void ratio, so it was not possible to measure the desired local void ratio distribution.

[Purpose of the invention]

An object of the present invention is to provide a method for measuring a local void fraction distribution that makes it possible to measure the local void fraction distribution with high accuracy.

[Summary of the invention]

The method for measuring a local void fraction distribution according to the present invention includes a radiation source that emits X-rays or γ-rays, a detector provided on a side facing the radiation source and a subject, and the detector and the radiation source. A method for measuring local void fraction distribution, comprising: a drive device for moving the drive device; and a control device for controlling the drive device; Before starting the measurement, the projection data acquisition time is determined in advance, and based on the determined acquisition time, the control device controls the drive device to scan the radiation source and the detector to obtain the local void fraction distribution. This is the configuration for performing measurements.

In other words, in the case of gas-liquid two-phase flow, the flow conditions (flow rate, pressure,
As long as the temperature (temperature) is constant, there is a time-averaged value of the local void fraction in any flow, and the projection data also converges to a constant value after a certain period of time. Therefore, the projection time for converging to the above-mentioned constant value is determined before starting the measurement, and the driving device is controlled in accordance with this projection time to scan the radiation source and the detector.

Therefore, it is possible to obtain time-average projection data even for a flowing object that changes with each measurement, and to measure the local void fraction distribution with high accuracy.

[Embodiments of the invention]

A first embodiment of the present invention will be described below with reference to FIGS. 2 to 6. First, with reference to Figures 2 to 4, an X-ray combinator tomography device (hereinafter referred to as a CT scanner)
The measurement principle will be explained. Generally, in a CT scanner, an X-ray tube and an X-ray detector (a combination of a scintillator such as NaI or BGO and a photomultiplier tube) are placed facing each other with the subject at the center, and a thin X-ray beam called a pencil beam is placed.
A beam of rays passes through the object and is incident on an x-ray detector. And as shown in Fig. 2, the X-ray tube 102 and the detector 103
unite to perform a linear scan (tran) on the subject 101.
slate operation) and a large number of xg distributed at equal intervals in parallel.
Obtain projection data. Next, as shown in FIG. 3, the subject 101 is rotated by a small angle (Rotate operation). Then, linear scanning is performed again to collect projection data. These two operations are then repeated alternately, and the measurement ends when the X-ray tube 102 and detector 103 are finally rotated by 180 degrees with respect to the subject 10. This measurement force method uses translation/rotation (translate ~ r
This method is called the "rotate" method. In addition to this translation/rotation method, there are rotation methods, but all currently developed CT scanners are of a method that measures projection data at different angles at different times.

Based on the measured projection data, an image reconstruction algorithm is used to calculate the linear absorption coefficient distribution of 7 otons using the X-
Consider a 7-coordinate system. At this coordinate (X, y), the distribution of the X-ray absorption coefficient is f(X, y), and the above-mentioned object 10
1 is divided into several pixels (i, j) 105, and the X-ray absorption coefficient at the pixel (i, j) 711J5 is assumed to be μij. Next, consider an X-Y coordinate system that is tilted by an angle θ with respect to the x-y coordinate system. And the strength is 1 parallel to the Y axis. If the X-ray beam 106 is irradiated, the X-ray intensity after passing through the subject 101 is 91. j, RJIi is a coefficient proportional to 107 in the plane through which the X-ray beam 106 passes through each pixel. Natural logarithm transformation of the attenuation rate of this X-ray intensity p(x
, θ)108 becomes. This p(x, θ) is referred to as projection data, and from this projection data, an image reconstruction algorithm such as a back projection method or a convolution method is used to calculate the 6 X-ray absorption coefficient distributions j. In this case, there is a linear relationship between the X-ray absorption coefficient distribution μlj and the density distribution ρlj or the local void fraction distribution αij in the case of a phase flow.

When measuring a fluid object such as a two-phase flow using the above-mentioned translational/rotational force OCT scanner, the X-ray absorption coefficient distribution μi obtained by the image reconstruction algorithm
j Also, no reproducibility is observed in the void fraction distribution α1j. In other words, in each measurement, variations can be seen in the values. This is because the projection data, which is the basis of the CT measurement, fluctuates due to temporal fluctuations due to the flow of the two-phase flow. In other words, projection data p(x, θn) and p(x,
θm) is an image of a different cross section because the two-phase flow is a flow that changes every moment. However, as mentioned above, in a gas-liquid two-phase flow, as long as the flow conditions (flow rate, pressure, temperature) are constant, a time average value of the local void fraction exists in any flow. The present embodiment focuses on this point and measures the local void ratio distribution.The time for the projection data to converge to a constant value is measured in advance, and the measurement is performed in accordance with this time.

FIG. 5 is a diagram showing a schematic configuration of a local det rate distribution measuring device according to this embodiment. In the figure, reference numeral 111 indicates a pipe as an object to be inspected, and a two-phase flow including voids as a gas phase flows within this pipe 11. In order to measure the local void fraction distribution of the two-phase flow in this piping 111, a CT scanner device 1 is used.
12 are provided. That is, on one side of the pipe 1110 in the radial direction, X-rays or γ
A radiation source 113 that emits radiation is installed, and this radiation source 11
A detector 114 is installed on the opposite side with the pipe 111 in between. These radiation sources 113 and detectors 114
are integrated via a pedestal frame 115, and are configured to perform translational and rotational movement (or only rotational movement) by a drive device 116 connected to this pedestal frame 115. Further, the radiation source 113, detector 114, and drive device 116 are connected to a control circuit 117. This control circuit 117 controls the drive device 116 to control the radiation source 113.
It also has a function of moving the detector 114 and calculating the linear absorption distribution of photons from the collected projection data using an image reconstruction algorithm.

In addition to the CT scanner device 112, X-ray (or
Line) A 萱meter 118 is installed. This density meter 118
The configuration is such that the projection data measurement time is determined in advance before starting the measurement. The X-ray (or γ-ray) density meter L is composed of a radiation source 119 that emits X-rays or γ-rays, and a detector 120 installed on the opposite side of the radiation source 119 and the piping 111. dress up These sources 11
9 and a detector 120 are also connected to the control circuit 117.

The measurement method will be explained based on the above configuration.

As shown in the flowchart of FIG. 6, projection data for a continuous angle θ0 is first measured by the density meter 118 and inputted to the control circuit 117. Control circuit 117
Based on this projection data, calculate the time integrated value of the projection data for each measurement time. At that time, the time integrated value is several mBeQ
If the time average value converges within a certain value (ε) in the next step, the time at that time is set as the collection time of the projection data. In other words, when two projection data are temporally adjacent, I P s (X'θo)Pg(X・θo)1×εXI
If P, (X-θo) 0.001<ε 0.1 holds true, then T2 at this time is determined as the measurement time of the projection data. The above judgment value (ε) is
It is determined by taking into account statistical errors in ray (or γ-ray) photons and variations in flow conditions of the object. Once the measurement time of the projection data is determined in this way, the measurement is started. First, the control circuit 117 controls the drive device 116 to control the speed of the translational or rotational movement of the gantry frame 115 to perform measurement so that the measurement time of one point of projection data matches the determined measurement time. The data detected at each projection point is time-averaged projection data, and the control circuit 117 uses this data to calculate the time-averaged local photon absorption coefficient distribution, local density distribution, and local id rate distribution. Ru.

That is, before starting the measurement, the measurement time of the projection data is measured by the density meter 118, and the control circuit 117 controls the drive device 116 to perform translational or rotational movement of the gantry frame 115 to match the measurement time. The data obtained at each projection point is time-averaged projection data, and therefore, based on this projection data, the time-averaged photon line absorption coefficient distribution, local density distribution, The local void fraction distribution can be adjusted with high precision. □ Next, a second embodiment will be described with reference to FIGS. 7 and 8. That is, in the first embodiment, a density analyzer 118 is provided as a means for measuring the projection data measurement time, and the measurement is performed using the density meter 118, but in the second embodiment, the projection data is measured using the CT scanner device 112. This configuration measures data measurement time. That is, as shown in the flowchart of FIG. 8, the CT scanner 112 is stopped at an appropriate position, and continuous projection data at an angle θ0 is measured and input to the control circuit 117. The control circuit 1 NOA calculates a time integrated value of projection data for each measurement time based on this input data. At this time, the integrated value is treated as discrete data at intervals of about several m5ec. and two that are adjacent in time
Compare the two projection data and if they match within a certain judgment value, it is determined that the integrated value has converged to a constant value, and the measurement time at this time is determined as the measurement time of 1120 projection data points on the CT scanner equipment. do. Once the projection data measurement time is determined, the measurement is started in the same way as in the first embodiment, and the control circuit 117 controls the drive device 116 to control the speed of the translational or rotational movement of the gantry frame 115 to measure the projection data points. Measurement is performed by adjusting the time to the determined measurement time. Then, based on the obtained time-averaged projection data, time-averaged local 7-year-old absorption coefficient distribution, local density distribution, and local void fraction distribution are calculated. Therefore, the same effects as in the embodiment described above can be achieved.

It should be noted that the same parts as in the previous embodiment are denoted by the same reference numerals, and the explanation of the same constituent parts is omitted.

〔Effect of the invention〕

As detailed above, according to the measurement force method of local void fraction distribution according to the present invention, in the case of gas-liquid two-phase flow, the flow conditions (flow rate,
Focusing on the fact that as long as the pressure and temperature (pressure and temperature) are constant, there is a time-averaged value of the local void fraction for any flow, and that the projection data also converges to a constant value after a certain period of time, the above Since the projection time to converge to a constant value is determined and the radiation source and detector are scanned in accordance with this projection time, time-averaged projection data can be obtained even for flowing objects that fluctuate from measurement to measurement. Local void fraction distribution can be measured with high precision.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the measurement principle of the X-ray transmission method showing a conventional example, Figs. 2 to 6 are diagrams showing a first embodiment of the present invention, and Figs.
4 to 4 are measurement principle diagrams showing the measurement principle of CT scan, FIG. FIG. 8 is a diagram showing the second embodiment, FIG. 7 is a schematic configuration diagram of the measuring device, and FIG. 8 is a flowchart diagram. 111... Piping (subject), 112... CT scanner device, 113... Radiation source, 114... Detector, 11
6... Drive device, 117... Control circuit. Applicant's agent Patent attorney Suzue Takehiko No. 11 2m Figure 3 - Figure 4 ■ Figure 5 H J Figure 6wI Figure 7 L J Figure 8

Claims (1)

[Claims] A radiation source that emits X-rays or gamma rays, a detector provided on the opposite side of the radiation source and the subject, a drive device that moves the detector and the radiation source, and a drive device that controls the drive device. In a local void ratio distribution measuring method in which a local void ratio distribution of a subject is measured by scanning a detector and a radiation source using the drive unit, the projection data is A collection time is determined, and the control device controls a drive device based on the determined collection time to scan the radiation source and the detector to measure the local void fraction distribution. A method for measuring local void fraction distribution.